I'd be thankful for your help. i created a point layers of store locations and customers in Florida by given coordinates (WGS 84 EPSG: 4326). Now i need a distance matrix between stores and customers but the result is in decimal degrees i think. I understand i have to reproject the 2 layers so that i can work with meter but how dows this work in QGIS? Which projection should i use and which setting should i use?
You have to reproject your coordinates to a cartesian system, like UTM. To do this, first, look at the UTM zone for your region, for example in this site and take note of the EPSG or Proj4 definition. Then, in QGIS, save the vector layer with another name, using "save as". You will be given the opportunity to specify a new SRS. Lastly, open the new layer and compute the new distance matrix. It will give you the results in meters.